Diets of Nesting Swainson\u27s Hawks in Relation to Land Cover in Northwestern North Dakota

Relationships between land use practices and types of prey used by Swainson\u27s hawks (Buteo swainsoni) in the Northern Great Plains is of increasing interest as the quantity and quality of habitat in the region declines. I recorded 1,284 prey items at 18 Swainson\u27 s hawk nesting areas throughout northwestern North Dakota during summer 1986-1987. After correcting for detectability biases and food needs of adults, I estimated (90% CI) 2,087-2,859 total prey individuals and 138.3-206.7 kg of prey biomass (x = 69.8 g/item) were consumed by adult and nestling Swainson\u27s hawks during my study. Major prey (\u3e10% overall frequency or biomass) were small «50 g) rodents, ground squirrels (Spermophilus spp.), juvenile ducks (Anatinae), juvenile galliforms, and amphibians. Wetland-dependent species composed nearly 50% of all identified prey items based on frequency and biomass though wetlands averaged only 18% ofland cover in Swainson\u27s hawk nesting areas (i.e., within 1 km of nests). Compared to previous studies in the region, I documented a greater diversity of prey items, with a lower proportion of Richardson\u27s ground squirrels (S. richardsonii) and higher proportions of small rodents, avian prey, and amphibians. Relationships between land cover in Swainson\u27s hawk nesting areas and composition of prey items used by nesting pairs indicated that fragments of grazed prairie, hay land, and especially wetland may enhance future conservation efforts for the hawk in intensively farmed landscapes throughout the Northern Great Plains